Swimmers, boaters and fishermen are being warned to stay away from a diesel fuel spill in a northwest Iowa lake.

Staff for the City of Storm Lake are trying to contain the diesel fuel spill on Storm Lake, but winds have carried some of the diesel to the lake’s east shoreline. The Iowa Department of Natural Resources is urging “people and pets” to avoid areas of the lake where there’s a “visible sheen on the water” — indicating there’s diesel fuel there.

Officials don’t know how much diesel was spilled. It happened when city staff were fueling up a pump that dredges silt off the lake bed.